On Jul 13, 2010, at 2:55 PM, Brendan Kenny wrote:
> On Tue, Jul 13, 2010 at 3:21 PM, L. David Baron <dbaron@dbaron.org> wrote:
>> On Tuesday 2010-07-13 07:15 -0700, Brad Kemper wrote:
>>> Arguments in favor of the distance measuring the Entire blur region width (current spec language):
>>>
>>> 1) The entire perimeter is blurred, outer and inner, not just
>>> outer, so it is logical that the width of the entire blur effect
>>> width should match the authored value.
>>
>> However, for 'text-shadow' the value is called the "blur radius",
>> not the "blur diameter" (and has been called "blur radius" since
>> http://www.w3.org/TR/1998/REC-CSS2-19980512/text.html#text-shadow-props ).
>>
>> (I'm not sure when the definition of 'box-shadow' changed from using
>> the commonly-used term "blur radius" to using the new term "blur
>> distance".)
>>
>> I'd also note that blurring is implemented as a generic
>> transformation of images; it's not just something applied to edges.
>> In that form, I think measuring in terms of the radius
>> (approximating the concept of how far away from its original
>> location can the color of a point can get) makes more sense than
>> using the diameter (approximating the distance between the two
>> farthest points in opposite directions that the color of a pixel can
>> reach).
>>
>> So I also favor switching the definition of box-shadow to match
>> text-shadow and to describe a blur radius rather than a diameter.
>
>
> "blur distance" was added very recently, I think just a few messages
> before it was realized that the change would be an issue:
>
> http://dev.w3.org/cvsweb/csswg/css3-background/Overview.src.html.diff?r1=1.232&r2=1.233&f=h
>
> "blur radius" had been replaced with "blur value" the revision before that.
The reason that it was changed from a radius is that Brad thought that it should be described, and defined in terms of its appearance, not in terms of the underlying implementation.
However, I'm with David. Blurring is a common graphical technique which is always based on filtering via a gaussian blur, for which the blur radius is an input parameter. I see nothing wrong with calling it a 'radius' in the spec.
Simon